String Melting Version Research Articles

Predictions forsNN=5.02TeV Pb + Pb collisions from a multiphase transport model

We present predictions from the string melting version of a multi-phase transport model on various observables in Pb+Pb collisions at $\sqrt {s_{NN}}=5.02$ TeV. We use the same version of the model as an earlier study that reasonably reproduced dN/dy, $p_{\rm T}$-spectra and elliptic flow of charged pions and kaons at low-$p_{\rm T}$ for central and semi-central heavy ion collisions at 200 GeV and 2.76 TeV. While we compare with the already-available centrality dependence data on charged particle $dN/d\eta$ at mid-pseudorapidity in Pb+Pb collisions at 5.02 TeV, we make predictions on identified particle dN/dy, $p_{\rm T}$-spectra, azimuthal anisotropies $v_n (n=2,3,4)$, and factorization ratios $r_{n}(\eta^{a},\eta^{b}) (n=2,3)$ for longitudinal correlations.

ϕ-meson production at forward/backward rapidity in high-energy nuclear collisions from a multiphase transport model

Within the framework of a multiphase transport model (AMPT), the $\phi$-meson production is studied in d+Au collisions at \srt = {200} GeV in the forward (d-going, $1.2<y<2.2$) and backward (Au-going, $-2.2<y<-1.2$) direction. The AMPT model with string melting version (parton cascade turning-on) describes the experimental data well, while the pure hadronic transport scenario of the AMPT model underestimates the $\phi$-meson production rate in comparison with the data. Detailed investigations including the rapidity, transverse momentum and collision system size dependencies of $\phi$-meson nuclear modification factor indicate that a combination of the initial state effect and a follow-up parton cascade is required in the AMPT model to describe the data. Similar calculations are also present in p+Pb collisions at \srt = {5.02} TeV and p+p collisions at \srt = {2.76} TeV. The findings from a comparison of AMPT model study with the data are consistent with that at RHIC energy.

Scaling of elliptic flow in heavy-ion collisions with the number of constituent quarks in a transport model

We studied the number of constituent quark scaling (NCQ) behaviour of elliptic flow ($v_{2}$) under the framework of A Multi-Phase Transport model (AMPT) at both top-RHIC and LHC energies. The NCQ-scaling in $v_{2}$ holds at top-RHIC energy with AMPT string melting version, while it breaks in Pb+Pb collisions at LHC energy using the same framework. The breaking of NCQ-scaling at LHC energy has been studied by varying the magnitude of parton-parton scattering cross-section and lifetime of hadronic cascade as implemented in AMPT. We find that the breaking of NCQ scaling in Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV is independent of the magnitude of parton-parton cross-section and the later stage hadronic interactions. Further we observed that scaling holds in a small collision system like Si+Si at $\sqrt{s_{NN}}$ = 2.76 TeV. We discussed that the breaking of NCQ scaling is possibly due to high phase-space density of constituents quarks in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.

Anisotropic Flow of Identified Hadrons by the Event Plane Method at FAIR Energies

A comprehensive study of the elliptic flow of hadrons for non central Au+Au collision with the impact parameter of b =5-9 fm in the mid rapidity region of (-1 ≤ ycm ≤1) with the reaction plane angle Ψ in the mid-pseudorapidity of |ɳ| < 0.35 is investigated in the FAIR energy regime of 25 A Gev by the AMPT model with both the default and the string melting scenarios. In both the versions of AMPT model, we have observed that at low PT regions up to PT ≈ 1.0 GeV/c, elliptic flow shows an almost linear increase with the increase in the transverse momentum. Also, there is a clear mass ordering effect that is particles with higher mass shows a smaller at a given PT than the particles with lower mass. In addition, the constituent quark number scaling of elliptic flow has been investigated where we have observed a universal scaling in the string melting version of the AMPT model i.e with the partonic degrees of freedom due to quark coalescence model compared with the default version of the AMPT model. Further, the scaling behavior has been observed for the transverse kinetic energy with both scenarios.

Evolution of transverse flow and effective temperatures in the parton phase from a multiphase transport model

I study the space-time evolution of transverse flow and effective temperatures in the dense parton phase with the string melting version of a multi-phase transport model. Parameters of the model are first constrained to reproduce the bulk data on the rapidity density, $p_{\rm T}$ spectrum and elliptic flow at low $p_{\rm T}$ for central and mid-central Au+Au collisions at $200A$ GeV and Pb+Pb collisions at $2760A$ GeV. I then calculate the transverse flow and effective temperatures in volume cells within mid-spacetime-rapidity $|\eta|<1/2$. I find that the effective temperatures extracted from different variables, which are all evaluated in the rest frame of a volume cell, can be very different; this indicates that the parton system in the model is not in full chemical or thermal equilibrium locally, even after averaging over many events. In particular, the effective temperatures extracted from the parton energy density or number density are often quite different than those extracted from the parton mean $p_{\rm T}$ or mean energy. For these collisions in general, effective temperatures extracted from the parton energy density or number density are higher than those extracted from the parton mean $p_{\rm T}$ in the inner part of the overlap volume, while the opposite occurs in the outer part of the overlap volume. I argue that this indicates that the dense parton matter in the inner part of the overlap volume is over-populated; I also find that all cells with energy density above 1 GeV/fm$^3$ are over-populated after a couple of fm/$c$.

Elliptic flow ofϕmesons as a sensitive probe for the onset of the deconfinement transition in high energy heavy-ion collisions

Elliptic flow (v_2) of \phi-meson is shown to be a sensitive probe of the partonic collectivity using A Multi Phase Transport (AMPT) model. Within the ambit of the AMPT model with partonic interactions (string melting version), the \phi-meson v_2 at midrapidity is found to have negligible contribution from hadronic interactions for Au+Au collisions at 200 GeV per nucleon. Changing the hadron cascade time in the model calculations does not change the \phi-meson v_2, while it reduces the v_2 of proton at low transverse momentum (pT). These observations indicate that a substantial reduction in \phi-mesons v_2 as a function of colliding beam energy would suggest the dominance of hadronic interactions over partonic interactions.